The present invention relates to an ink liquid supply system for an ink jet system printer and, more particularly, to an ink liquid supply system which holds the concentration of the ink liquid at a constant value.
In general, in an ink jet system printer, ink droplets from a nozzle are issued toward a recording paper, and then desired ink droplets are deflected in a desired direction when they pass through an appropriate deflection means. The deflected ink droplets are deposited on the recording paper in order to record desired symbols corresponding to printing information supplied. In an ink jet system printer of the charge amplitude controlling type wherein an ink stream from a nozzle having an ultrasonic vibrator is broken into ink droplets at a given vibration frequency, and the individual ink droplets, being charged by a charging electrode in accordance with printing information, are deflected in accordance with the amplitude of charges carried thereon as they pass through an electrostatic field of a fixed high voltage thereby printing desired symbols such as alphabet characters, it is especially important that the application of charging signals is accurately timed to be in agreement with the droplet separation phase. Therefore, it is necessary to hold the pedetermined phase relationship between the droplet separation and the ultrasonic vibration substantially constant. In the ink jet system printer of the charge amplitude controlling type, the ink droplets are always emitted from the nozzle while the ink jet system printer is in the operative condition. The ink droplets not utilized in the writing operation are neither charged nor deflected and are directed to a beam gutter in order to recirculate the waste ink liquid to an ink liquid reservoir. The thus recirculated ink liquid has a high concentration, since a portion of the volatile component of the ink liquid volatilizes while the ink droplets travel through the air from the nozzle to the beam gutter. Accordingly, the concentration of the ink liquid contained in the ink liquid supply system gradually increases during the operation of the ink jet system printer.
The increase of the ink liquid concentration will create variations of the print quality, and will vary the drop formation phase. This is not preferable for the ink jet system printer of the charge amplitude controlling type, because the phase relationship between the droplet separation and the ultrasonic vibration must be maintained constant in this type of ink jet system printer.